1. Field of the Invention
The present invention relates to fuel supply apparatus for supplying fuel to an internal combustion engine of a vehicle, such as an automobile. In particular, the present invention relates to fuel supply apparatus having a pressure regulator that can adjust a pressure of fuel pumped by a fuel pump.
2. Description of the Related Art
A known fuel supply apparatus disclosed in Japanese Laid-Open Patent Publication No. 2002-235622 includes a fuel pump and a pressure regulator. The fuel pump feeds fuel to an internal combustion engine under pressure. The pressure regulator (pressure regulating valve) can regulate a pressure level of the fuel discharged from the fuel pump to a high level or a low level. The fuel pump and the pressure regulator are modularized and are disposed within a fuel tank. The fuel pump and the pressure regulator communicate with each other via a communication pipe. The communication pipe is branched from a fuel delivery pipe. The fuel delivery pipe communicates between the fuel pump and an injector(s) that can inject fuel into the engine. Therefore, a part of the fuel discharged from the fuel pump is supplied to the pressure regulator where the pressure is adjusted. The pressure regulator includes a first pressure chamber and a second pressure chamber. A return pipe is connected to the first pressure chamber for returning the fuel into the fuel tank. The second pressure chamber has a bag-like configuration with no fuel outlet. A diaphragm separates the first chamber and the second chamber from each other and supports a valve member that is operable to open and close an opening of the return pipe. A first introduction pipe and a second introduction pipe are branched from the fuel delivery pipe. The pressure of the fuel discharged from the fuel pump is directly applied to the first pressure chamber via the first introduction pipe. The fuel supplied to the first pressure chamber returns into the fuel tank via the return pipe. The fuel is supplied to the second pressure chamber via the second introduction pipe. However, the return pipe also communicates with the second introduction pipe in a branched manner, so that a part of the fuel supplied from the fuel delivery pipe returns into the fuel tank via a throttle. Therefore, the second pressure chamber receives a middle pressure that has an intermediate value between the discharge pressure of the fuel pump and the pressure within the fuel tank.
Another known fuel supply apparatus disclosed in Japanese Laid-Open Patent Publication No. 64-32066 includes a fuel pump and a pressure regulator that are positioned outside of a fuel tank. In this publication, the pressure regulator regulates the fuel pressure by using the pressure of the fuel discharged from the fuel pump, the atmospheric pressure and a negative pressure at an air intake port. More specifically, the pressure regulator includes a first negative pressure chamber, a second negative pressure chamber and a fuel chamber. The first negative pressure chamber and the second negative pressure chamber are separated from each other by a first diaphragm. The second negative pressure chamber and the fuel chamber are separated from each other by a second diaphragm that has a pressure receiving area smaller than a pressure receiving area of the first diaphragm. A first changeover device and a second changeover device each configured as a three-way valve are associated with the first negative pressure chamber and the second negative pressure chamber, respectively, so that the first negative pressure chamber and the second negative pressure chamber can selectively communicate with either of a negative pressure introduction pipe for introducing the negative pressure from the air intake port, a negative pressure communication pipe communicating with a negative pressure tank that accumulates the negative pressure applied from the air intake port, and an atmospheric pressure introduction port. A part of the fuel pumped by the fuel pump is always supplied to the fuel chamber. For setting the fuel pressure to a high level when the fuel is at a high temperature, the atmospheric pressure is introduced into the first negative pressure chamber, and the negative pressure is introduced from the negative pressure tank into the second negative pressure chamber. For setting the fuel pressure to a middle level when the fuel is at a middle temperature, the atmospheric pressure is introduced into both of the first negative pressure chamber and the second negative pressure chamber. For setting the fuel pressure to a low level when the fuel is at a low temperature, the negative pressure from the air intake port is introduced into both of the first negative pressure chamber and the second negative pressure chamber. In this way, it is possible to adjust the pressure of the fuel pumped by the fuel pump to the high level, the middle level or the low level.
In the case of the arrangement of the Publication No. 2002-235622, the pressure is adjusted using only the pressure of the fuel discharged from the fuel pump. Therefore, the pressure regulator and the fuel pump can be modularized and can be disposed within the fuel tank. Hence, it is possible to save the installation space. However, because the pressure regulator has only the first and second pressure chambers separated by the first diaphragm, the fuel pressure can be adjusted to only two different pressure levels, i.e., the high level and the low level. In addition, although the middle pressure between the discharge pressure of the fuel pump and the pressure within the fuel tank is applied to the second pressure chamber, the middle pressure is produced by the throttle that is provided across the branch point between the second introduction pipe and the return pipe, and the second chamber has a bag-like configuration with no fuel outlet. Therefore, there is a possibility that the vapor produced within the fuel may stay within the second pressure chamber to cause improper pressure adjustment.
In the case of the arrangement of the Publication No. 64-32066, the pressure regulator includes the first negative pressure chamber, the second negative pressure chamber and the fuel chamber that are separated from each other by the first and second diaphragms having different pressure receiving areas. Therefore, it is possible to adjust the pressure of the fuel to three different pressure levels including the high level, the middle level and the low level. However, in this publication, the fuel pressure is adjusted by using the pressure of the fuel, the atmospheric pressure and the negative pressure of the air intake pipe. Therefore, it is not possible to modularize the fuel pump and the pressure regulator. For this reason, the fuel pump and the pressure regulators are disposed outside of the fuel tank. This may lead to increase the size of the system. In addition, the first changeover device, the second changeover device, the negative pressure tank, etc., are required for selectively introducing the atmospheric pressure and the negative pressure of the air intake pipe into each of the first and second negative pressure chambers. Therefore, the number of components required for the system is large, and the piping paths are complicated. Further, for achieving the high pressure level, the fuel pressure is applied to the fuel chamber, while the atmospheric pressure and the negative pressure are applied to the first negative pressure chamber and the second negative pressure chamber, respectively. Therefore, a maximum pressure value that can be achieved by this arrangement may be no more than a value that slightly exceeds the sum of the usually applied pressure and the atmospheric pressure. Furthermore, according to this publication, the pressure receiving area of the second diaphragm is smaller than the pressure receiving area of the first diaphragm. No other arrangement is disclosed in this publication.
Therefore, there is a need in the art for fuel supply apparatus that can achieve at least three different pressure levels while enabling modularization of a fuel pump and a pressure regulator.